Although the incidence of degenerative changes in the blood vessels is well known to increase with advancing age, quantitative data on the peripheral blood flow due to the aging process per se are lacking. Venous occlusion plethysmography has been shown to be the most accurate and reproducible method to measure the peripheral blood flow. We used this method to evaluate peripheral blood flow in the subjects of the Baltimore Longitudinal Study of Aging with ages ranging from 20 to 83 years. The study was designed to evaluate the effect of age on peripheral blood flow by venous occulsion plethysmography during rest and in response to removal of arterial occlusion and thermal stress which result in maximal flow.